/*
**
** This header file (together with is companion C source-code file "os.c") attempt to abstract the underlying operating system so that
** the APPID library will work on both POSIX and windows systems.
**
** This header file is #include-ed by System.h and thus ends up being included by every source file.
*/
#ifndef _SYSTEM_OS_H_
#define _SYSTEM_OS_H_

/*
** Figure out if we are dealing with Unix, Windows, or some other operating system.  After the following block of preprocess macros,
** all of SQLITE_OS_UNIX, SQLITE_OS_WIN, SQLITE_OS_OS2, and SQLITE_OS_OTHER  will defined to either 1 or 0.  One of the four will be 1.  The other 
** three will be 0.
*/
#if defined(SYSTEM_OS_OTHER)
# if SYSTEM_OS_OTHER==1
#   undef SYSTEM_OS_UNIX
#   define SYSTEM_OS_UNIX 0
#   undef SYSTEM_OS_WIN
#   define SYSTEM_OS_WIN 0
#   undef SYSTEM_OS_OS2
#   define SYSTEM_OS_OS2 0
# else
#   undef SYSTEM_OS_OTHER
# endif
#endif
#if !defined(SYSTEM_OS_UNIX) && !defined(SYSTEM_OS_OTHER)
# define SYSTEM_OS_OTHER 0
# ifndef SYSTEM_OS_WIN
#   if defined(_WIN32) || defined(WIN32) || defined(__CYGWIN__) || defined(__MINGW32__) || defined(__BORLANDC__)
#     define SYSTEM_OS_WIN 1
#     define SYSTEM_OS_UNIX 0
#     define SYSTEM_OS_OS2 0
#   elif defined(__EMX__) || defined(_OS2) || defined(OS2) || defined(_OS2_) || defined(__OS2__)
#     define SYSTEM_OS_WIN 0
#     define SYSTEM_OS_UNIX 0
#     define SYSTEM_OS_OS2 1
#   else
#     define SYSTEM_OS_WIN 0
#     define SYSTEM_OS_UNIX 1
#     define SYSTEM_OS_OS2 0
#  endif
# else
#  define SYSTEM_OS_UNIX 0
#  define SYSTEM_OS_OS2 0
# endif
#else
# ifndef SYSTEM_OS_WIN
#  define SYSTEM_OS_WIN 0
# endif
#endif

/*
** Determine if we are dealing with WindowsCE - which has a much reduced API.
*/
#if defined(_WIN32_WCE)
# define SYSTEM_OS_WINCE 1
#else
# define SYSTEM_OS_WINCE 0
#endif

/*
** Define the maximum size of a temporary filename
*/
#if SYSTEM_OS_WIN
# include <windows.h>
# define SYSTEM_TEMPNAME_SIZE (MAX_PATH+50)
#elif SYSTEM_OS_OS2
# if (__GNUC__ > 3 || __GNUC__ == 3 && __GNUC_MINOR__ >= 3) && defined(OS2_HIGH_MEMORY)
#  include <os2safe.h> /* has to be included before os2.h for linking to work */
# endif
# define INCL_DOSDATETIME
# define INCL_DOSFILEMGR
# define INCL_DOSERRORS
# define INCL_DOSMISC
# define INCL_DOSPROCESS
# define INCL_DOSMODULEMGR
# define INCL_DOSSEMAPHORES
# include <os2.h>
# include <uconv.h>
# define SYSTEM_TEMPNAME_SIZE (CCHMAXPATHCOMP)
#else
# define SYSTEM_TEMPNAME_SIZE 200
#endif

/* If the SET_FULLSYNC macro is not defined above, then make it
** a no-op
*/
#ifndef SET_FULLSYNC
# define SET_FULLSYNC(x,y)
#endif

/*
** The default size of a disk sector
*/
#ifndef SYSTEM_DEFAULT_SECTOR_SIZE
# define SYSTEM_DEFAULT_SECTOR_SIZE 512
#endif

/*
** Temporary files are named starting with this prefix followed by 16 random alphanumeric characters, and no file extension. They are stored in the
** OS's standard temporary file directory, and are deleted prior to exit. If sqlite is being embedded in another program, you may wish to change the
** prefix to reflect your program's name, so that if your program exits * prematurely, old temporary files can be easily identified. This can be done
** using -DSQLITE_TEMP_FILE_PREFIX=myprefix_ on the compiler command line.
**
** 2006-10-31:  The default prefix used to be "sqlite_".  But then Mcafee started using SQLite in their anti-virus product and it
** started putting files with the "sqlite" name in the c:/temp folder. This annoyed many windows users.  Those users would then do a 
** Google search for "sqlite", find the telephone numbers of the developers and call to wake them up at night and complain.
** For this reason, the default name prefix is changed to be "sqlite" spelled backwards.  So the temp files are still identified, but
** anybody smart enough to figure out the code is also likely smart enough to know that calling the developer will not help get rid
** of the file.
*/
#ifndef SYSTEM_TEMP_FILE_PREFIX
# define SYSTEM_TEMP_FILE_PREFIX "etilqs_"
#endif

/*
** The following values may be passed as the second argument to systemOsLock(). The various locks exhibit the following semantics:
**
** SHARED:    Any number of processes may hold a SHARED lock simultaneously.
** RESERVED:  A single process may hold a RESERVED lock on a file at any time. Other processes may hold and obtain new SHARED locks.
** PENDING:   A single process may hold a PENDING lock on a file at any one time. Existing SHARED locks may persist, but no new
**            SHARED locks may be obtained by other processes.
** EXCLUSIVE: An EXCLUSIVE lock precludes all other locks.
**
** PENDING_LOCK may not be passed directly to systemOsLock(). Instead, a process that requests an EXCLUSIVE lock may actually obtain a PENDING
** lock. This can be upgraded to an EXCLUSIVE lock by a subsequent call to systemOsLock().
*/
#define NO_LOCK         0
#define SHARED_LOCK     1
#define RESERVED_LOCK   2
#define PENDING_LOCK    3
#define EXCLUSIVE_LOCK  4

/*
** File Locking Notes:  (Mostly about windows but also some info for Unix)
**
** We cannot use LockFileEx() or UnlockFileEx() on Win95/98/ME because those functions are not available.  So we use only LockFile() and
** UnlockFile().
**
** LockFile() prevents not just writing but also reading by other processes. A SHARED_LOCK is obtained by locking a single randomly-chosen 
** byte out of a specific range of bytes. The lock byte is obtained at random so two separate readers can probably access the file at the 
** same time, unless they are unlucky and choose the same lock byte. An EXCLUSIVE_LOCK is obtained by locking all bytes in the range.
** There can only be one writer.  A RESERVED_LOCK is obtained by locking a single byte of the file that is designated as the reserved lock byte.
** A PENDING_LOCK is obtained by locking a designated byte different from the RESERVED_LOCK byte.
**
** On WinNT/2K/XP systems, LockFileEx() and UnlockFileEx() are available, which means we can use reader/writer locks.  When reader/writer locks
** are used, the lock is placed on the same range of bytes that is used for probabilistic locking in Win95/98/ME.  Hence, the locking scheme
** will support two or more Win95 readers or two or more WinNT readers. But a single Win95 reader will lock out all WinNT readers and a single
** WinNT reader will lock out all other Win95 readers.
**
** The following #defines specify the range of bytes used for locking. SHARED_SIZE is the number of bytes available in the pool from which
** a random byte is selected for a shared lock.  The pool of bytes for shared locks begins at SHARED_FIRST. 
**
** The same locking strategy and byte ranges are used for Unix.  This leaves open the possiblity of having
** clients on win95, winNT, and unix all talking to the same shared file and all locking correctly.  To do so would require that samba (or whatever
** tool is being used for file sharing) implements locks correctly between windows and unix.  I'm guessing that isn't likely to happen, but by
** using the same locking range we are at least open to the possibility.
**
** Locking in windows is manditory.  For this reason, we cannot store actual data in the bytes used for locking.  The pager never allocates
** the pages involved in locking therefore.  SHARED_SIZE is selected so that all locks will fit on a single page even at the minimum page size.
** PENDING_BYTE defines the beginning of the locks.  By default PENDING_BYTE is set high so that we don't have to allocate an unused page except
** for very large databases.  But one should test the page skipping logic  by setting PENDING_BYTE low and running the entire regression suite.
**
** Changing the value of PENDING_BYTE results in a subtly incompatible file format.  Depending on how it is changed, you might not notice
** the incompatibility right away, even running a full regression test. The default location of PENDING_BYTE is the first byte past the
** 1GB boundary.
**
*/
#ifdef SYSTEM_OMIT_WSD
# define PENDING_BYTE     (0x40000000)
#else
# define PENDING_BYTE      systemPendingByte
#endif
#define RESERVED_BYTE     (PENDING_BYTE+1)
#define SHARED_FIRST      (PENDING_BYTE+2)
#define SHARED_SIZE       510

/*
** Wrapper around OS specific system_os_init() function.
*/
int systemOsInit(void);

/* 
** Functions for accessing system_file methods 
*/
int systemOsClose(system_file*);
int systemOsRead(system_file*, void*, int amt, i64 offset);
int systemOsWrite(system_file*, const void*, int amt, i64 offset);
int systemOsTruncate(system_file*, i64 size);
int systemOsSync(system_file*, int);
int systemOsFileSize(system_file*, i64 *pSize);
int systemOsLock(system_file*, int);
int systemOsUnlock(system_file*, int);
int systemOsCheckReservedLock(system_file *id, int *pResOut);
int systemOsFileControl(system_file*, int, void*);
#define SYSTEM_FCNTL_DB_UNCHANGED 0xca093fa0
int systemOsSectorSize(system_file *id);
int systemOsDeviceCharacteristics(system_file *id);
int systemOsShmMap(system_file*, int, int, int, void volatile**);
int systemsShmLock(system_file *id, int, int, int);
void systemOsShmBarrier(system_file *id);
int systemOsShmUnmap(system_file *id, int);

/* 
** Functions for accessing system_vfs methods 
*/
int systemOsOpen(system_vfs*, const char*, system_file*, int, int*);
int systemOsDelete(system_vfs*, const char*, int);
int systemOsAccess(system_vfs*, const char*, int, int *pResOut);
int systemOsFullPathname(system_vfs*, const char*, int, char*);
#ifndef SYSTEM_OMIT_LOAD_EXTENSION
void *systemOsDlOpen(system_vfs*, const char*);
void systemOsDlError(system_vfs*, int, char*);
void (*systemOsDlSym(system_vfs*,void*,const char*))(void);
void systemOsDlClose(system_vfs*, void*);
#endif
int systemOsRandomness(system_vfs*, int, char*);
int systemOsSleep(system_vfs*, int);
int systemOsCurrentTimeInt64(system_vfs*, INT64_TYPE*);

/*
** Convenience functions for opening and closing files using system_malloc() to obtain space for the file-handle structure.
*/
int systemOsOpenMalloc(system_vfs*, const char*, system_file**, int, int*);
int systemOsCloseFree(system_file*);

#endif /* _SYSTEM_OS_H_ */
